A copper alloy sheet having high electric conductivity and high strength has thus far been used as a constituent material for connectors, terminals, relays, springs, switches, semiconductors, lead frames and the like that are used in electric components, electronic components, vehicle components, communication devices, electric and electronic devices and the like. However, in response to a decrease in the size and weight and an improvement of the performance of such devices in recent years, there is a demand for extremely strict characteristic improvement with the constituent materials used for the above-described devices. For example, an extremely thin sheet is used in a spring contact section in a connector, and a high-strength copper alloy configuring the above-described extremely thin sheet is required to have high strength or a high degree of balance between elongation and strength to procure a thin thickness. Furthermore, the high-strength copper alloy is required to be excellent in terms of productivity and economic efficiency and to have no problems with electric conductivity, corrosion resistance (stress corrosion crack resistance, dezincification corrosion resistance and migration resistance), stress relaxation characteristics, solderability, and the like.
In addition, in the constituent material for connectors, terminals, relays, springs, switches, semiconductors, lead frames and the like that are used in electric components, electronic components, vehicle components, communication devices, electric and electronic devices and the like, there is a component and a section requiring higher strength or higher electric conductivity to satisfy the requirement of a thin thickness which is a precondition for excellent elongation and excellent bending workability. However, strength and electric conductivity are opposing characteristics, and thus the improvement of strength is generally followed by a decrease in electric conductivity. In the above-described circumstance, there is a component requiring a high-strength material having higher electric conductivity (approximately 30% IACS or higher, for example, approximately 36% IACS) at a tensile strength of, for example, 500 N/mm2 or more. In addition, there is a component requiring superior stress relaxation characteristics and superior thermal resistance since the component is used under a high-temperature environment such as near a vehicle engine room.
Well-known examples of a copper alloy having high electric conductivity and high strength generally include beryllium copper, phosphor bronze, nickel silver, brass and Sn-added brass. The above-described general high-strength copper alloys have the following problems, and cannot satisfy the above-described requirements.
Beryllium copper has the highest strength among copper alloys, but beryllium is extremely harmful to human bodies (particularly, in a molten state, even an extremely small amount of beryllium vapor is extremely dangerous). Therefore, disposal (particularly, incineration disposal) of a beryllium copper member or a product including a beryllium copper member is difficult, and the initial cost for a dissolution facility used for manufacturing becomes extremely high. Therefore, to obtain predetermined characteristics, it becomes necessary to carry out a solution thermal treatment in the final phase of manufacturing, and thus there is a problem with economic efficiency including the manufacturing costs.
Since phosphor bronze and nickel silver have poor hot workability, and are not easily manufactured through hot rolling, it is common to manufacture phosphor bronze and nickel silver through transverse continuous casting. Therefore, the productivity is poor, the energy cost is high, and the yield is also poor. In addition, since phosphor bronze for springs or nickel silver for springs which is a typical copper alloy having high strength contains a large amount of expensive Sn and Ni, the electric conductivity is poor, and there is a problem with economic efficiency.
Brass and Sn-added brass are cheap, but cannot satisfy the strength, have poor stress relaxation characteristics and poor electric conductivity, and have a problem with corrosion resistance (stress corrosion and dezincification corrosion), and therefore brass and Sn-added brass are not suitable as a constituent material for the above-described products requiring a decrease in size and an improvement of performance.
Therefore, the above-described general copper alloys having high electric conductivity and high strength can be by no means satisfactory as a constituent material for components of a variety of devices having a tendency of size decrease, weight decrease and performance improvement as described above, and there is a strong demand for development of a novel copper alloy having high electric conductivity and high strength.
As an alloy for satisfying the above-described requirement of high electric conductivity and high strength, for example, a Cu—Zn—Sn alloy as described in Patent Document 1 is known. However, the alloy according to Patent Document 1 is also not sufficient in terms of electric conductivity and strength.